With continuous upgrading of mobile communications systems, new performance requirements are raised for antennas. For example, multi-beam and miniaturization become main factors of modern antenna design. A multi-beam network is a main technology for implementing a multi-beam antenna by utilizing space selectivity. A method in which the space selectivity is utilized can bring benefits in two aspects: first, selective transmission and receiving are performed, so that interference to a neighboring cell and interference from the neighboring cell can be reduced, second, spatial multiplexing is formed among multiple beams.
A multi-beam antenna system includes two parts: one part is a dual-polarized array formed by dual-polarized antenna units, and the other part is a Butler (Butler) matrix, and the dual-polarized array is connected to the Butler matrix. The Butler matrix is a completely passive and reciprocal circuit, and the circuit includes several directional couplers and phase shift elements. The Butler matrix is configured to generate a beam, and the beam generated by the Butler matrix is transmitted by using the dual-polarized array. Currently, in a multi-beam antenna system application, same beams are used in two polarization directions to form a network; therefore, two polarizations exist in each beam direction (see FIG. 1). The foregoing multi-beam antenna system becomes a cross-polarization multi-beam antenna system. Effects of such a cross-polarization multi-beam antenna system are polarization diversity or multiplexing inside a beam and multiplexing among beams.
FIG. 1 shows multiple beams that are formed by a four-column dual-polarized antenna, where each polarization uses an amplitude and a phase in Table 1, and two polarizations both point to a same direction.
TABLE 1Column 1Column 2Column 3Column 4Beam 11   −2251   −1801   −1351   −90Beam 21   451   −901   −2251   0Beam 31   −2701   −1351   01   135Beam 41   01   −451   −901   −135
The cross-polarization multi-beam system is an orthogonal system, that is, each direction in which a maximum value is reached of a beam of each polarization is basically a null or a sidelobe of another beam of the same polarization. Main problems of the cross-polarization multi-beam system lie in: first, generally, when a relatively large quantity of multiple beams are formed in such a system, a quantity of stages of a multi-beam matrix increases, for example, a three-stage network needs to be used when six beams are to be formed, and when a quantity of network stages of increases, a machining difficulty and a network loss significantly increase; second, a sidelobe is difficult to be reduced, and sidelobe levels of two most-lateral beams are higher for a Butler-type matrix in general, and therefore interference between adjacent multiplexed beams increases.